The invention is directed to methods and systems for simultaneous real-time fluorescence and color video endoscopy at close to video frame rates. The invention is also directed to high-efficiency illumination sources and to methods and systems for controlling temporal and spectral output of these light sources.
Medical endoscopy is increasingly employing specialized optical imaging techniques, such as fluorescence (i.e. autofluorescence and photodynamic) endoscopy, narrow band imaging and other techniques, for improved visualization and for the detection and diagnosis of diseases, Endoscopic imaging systems that provide specialized imaging modes typically also operate in a conventional color, or white-light, endoscopy mode. Embodiments of endoscopic imaging systems incorporating both a color and fluorescence imaging modes have been disclosed, for example, in U.S. Pat. No. 6,462,770 B1, U.S. Pat. No. 6,821,245 B1, and U.S. Pat. No. 6,899,675 B2.
In conventional white-light endoscopy, hereinafter also referred to as color imaging mode, light in the visible spectral range is used to illuminate the tissue surface under observation. Light reflected by the tissue passes through a suitable lens system and is incident on an image sensor built into or attached to the endoscope. The electrical signals from the image sensor are processed into a full color video image which can be displayed on a video monitor or stored in a memory. In fluorescence endoscopy, fluorescence excitation light excites fluorophors in the tissue, which emit fluorescence light at an emission wavelength which is typically greater than the excitation wavelength. Fluorescence light from the tissue passes through a suitable lens system and is incident on the image sensor. The electrical signals from the image sensor are processed into a fluorescence video image which can be displayed on a video monitor, either separately from or together with the color video image, or stored in a memory.
The fluorescence excitation and emission wavelengths depend upon the type of fluorophors being excited. In the case of exogenously applied fluorophors, the band of excitation wavelengths may be located anywhere in the range from the ultraviolet (UV) to the near infra-red (NIR) and the emission wavelength band anywhere from the visible to the NIR. For fluorophors endogenous to tissue, the band of excitation and emission wavelengths are more limited (excitation from the UV to the green part of the visible spectrum, emission from the blue-green to the NIR).
In a conventional fluorescence/white-light endoscopic imaging system, the system can be switched between color and fluorescence modes either automatically or with a hand- or foot-operated external switch. Both the illumination and imaging characteristics of the endoscopic imaging system may require adjustment when switching the operation of an endoscopic imaging system from one mode to the other. For example, gain adjustments and additional image processing (e.g., pixel binning, time averaging, etc.) may be required because the image signal in color imaging mode tends to be substantially greater than the image signal from endogenous (tissue) fluorescence. Although switching between imaging modes with an automated device is not difficult, additional time may be required to complete the endoscopic procedure because areas of interest are examined sequentially in each mode.
It would therefore be desirable to provide an endoscopic imaging system capable of acquiring and displaying images in both conventional color (“white-light”) and fluorescence imaging modes simultaneously. It would further be desirable to employ high-efficiency illumination sources that can be easily controlled over the spectral range of interest for endoscopy.